TM 32-5835-001-24 & P
DIRECT
SUPPORT
AND
GENERAL
SUPPORT
MAINTENANCE
Section I.
PRINCIPLES OF OPERATION
section. The recorder set consists of two major assemblies: recorder and power
supply .
a.
Recorder.
(1) Recording technique. Standard direct recording techniques are used in
which a direct record amplifier records the time relationship of analog input signals
directly on magnetic tape. Basically, the record circuit is composed of two sections:
a data signal amplifier and a bias oscillator. The signal amplifier amplifies the input
signal and provides a current source to drive the record head with signals propor-
tional to the applied input signals. This creates, in the magnetic oxide coating of the
tape, magnetic flux changes which correspond in intensity and timing to the input
signals. Since the flux density in a magnetic medium does not vary linearly with the
magnetizing force, the data signal is superimposed on a high frequency (38 kHz) bias
signal to overcome the hysteresis nonlinearity of the magnetic tape. A symmetrical
low distortion bias signal is adjusted to optimize system parameters such as frequency
response, signal-tonoise ratio, and distortion. The data signal is adjusted for re-
cording at normal record level (3 percent third harmonic distortion upon reproduction
of a 400 Hz signal at an input record signal level of O dBm.) The bias and data sig
nal record levels are both a function of the characteristics of the record head and the
magnetic tape used and must be adjusted accordingly.
(2) Equalization technique. Two techniques are commonly used for direct re-
cording of signals on magnetic tape. One of these, known as constant flux recording
is used in instrumentation applications in which there is an equal probability of high
level signals at any frequency within the passband to be recorded. For audio appli-
cations, in which the spectral energy of the signal to be recorded diminished with in-
creasing frequency, a preemphasized or "pre-equalized" recording technique is used
to allow optimum utilization of the recording medium. Pre-emphasized recording is
the method used in this recorder.
(3) Recorder functional sections. Refer to figure 3-1. The recorder is func-
tionally divided into the electromechanical tape drive system, the control logic elec-
tronics, the data signal electronics, and the plug-in power supply. The recorder,
which is the major functional assembly, consists of a rigid chassis upon which all of
the required electronic subassemblies and the mechanical tape handling subassemblies
are mounted, enclosed in a protective housing. The chassis assembly and the control
panel (which form an integral component) slide into the case and are secured by four
screws. A gasket between the front panel and the case provides a moisture seal and
electrical continuity to prevent RFI radiation. The chassis provides mounting facilities
for an electromechanical capstan drive system, and electromechanical reel drive system,
and the modular electronic circuits to control the tape handling components and signal
processing.
Previous Page
